Surface radiation forum

Hi Theo,

excellent idea to evaluate the anomaly of surface radiation using the CM SAF climate data set as reference. To me the data you generated looks very reasonable, please keep in mind that the unit is W/m2, this might explain the low values (also, you looking at the UK, not Greece...)

To calculate the anomaly you can use the cdo ymonsub-operator in combination with the ymonmean, even in one line (if you have all the data merged into one file):

cdo ymonsub SIS_mm.nc -ymonmean SIS_mm.nc SIS_anomaly.nc

Anyway, it is still interesting to have a look at the climatological data as well...

Here is one note of caution:
The CM SAF climate data set (1983-2005) and the CM SAF operational data have been generated using different algorithms with different characteristics. For example, the climate data set tends to overestimate surface radiation by a few W/m2, while the operational product tends to underestimate SIS by a few W/m2. Hence, any difference you are getting is not necessarily related to a climatological anomaly, but can, at least in part, also be related to these differences in the retrieval (see the lecture by Rebekka Posselt: http://www.eumetrain.org/resources/surface_radiation_retrieval_2012.html)

In her presentation, Anke Kniffka, presented results from a comparison of the climate data set and the operational product for the end of 2005, when both data are available:

http://www.eumetrain.org/resources/operational_products_of_the_cm_saf_2012.html
https://classroom.eumetsat.int/pluginfile.php/7578/mod_resource/content/2/08_OperationalProducts_Kniffka.pdf (Slide 29)

This comparison might give you an indication on the size of the difference induced by the application of the different algorithms, any anomaly exceeding this threshold can then be regarded as an 'climatological anomaly'.

We are currently working towards a homogenization of the algorithms, i.e., in the future we will use the same algorithms for the operational product and the climate data records, which will then limit these problems.

Please note that anomalies of surface radiation are also reported by the Regional Climate Center - Climate Monitoring:
http://www.dwd.de/rcc-cm
Under Products -> Monitoring Europe -> Radiation you can find maps of anomalies of SIS also based on CM SAF data, however, using an climatology based on GEWEX-SRB data, adjusted to the CM SAF data. Only three classes are reported: negative, neutral, positive.

Kind regards,
Jörg